Table of contentsIntroductionSynthesis techniquesCarbon arc dischargeLaser ablationChemical vapor deposition (CVD)Characterization of carbon nanotube-based pressure sensorsScanning electron microscopyResistance relationships - pressurePressure sensing mechanismApplicationConclusionPressure sensors are very essential and are used in various fields such as aerospace, barometry, industrial, automobile, medical, etc. Carbon nanotube is one of the materials used to design the pressure sensor with the appropriate substrate material such as silicon used for a certain application. In this theoretical study, the synthesis, characterization and analysis of CNTs for pressure sensing were carried out. Due to its high gauge factor (200 to 1000), high sensitivity, temperature independence and many other advantages, CNT is a very effective material for use as a piezoresistive element in pressure sensors piezoresistive. Say no to plagiarism. Get Custom Essay on “Why Violent Video Games Should Not Be Banned”?Get Original EssayIntroductionThe discovery and development of the nanoworld has played a huge role in the scientific and technological progress of the universe. Nanomaterials have received the most attention since their discovery and they can be distinguished and classified based on their dimensionality (0D, 1D, 2D and 3D). They are also the most studied due to their unique electrical, mechanical, optical and magnetic properties. a wide range of applications they offer. Recently, various nanomaterials have attracted interest, including nanowires, carbon nanotubes, polymer nanofibers, metal nanoparticles, and graphene, which have been used for the fabrication of novel flexible pressure and strain sensors. These nanomaterials have potential applications such as flexible touchscreens, soft robotics, electronic skin, and energy harvesting. So far, pressure sensors work on force-induced changes in capacitance, piezoelectricity, triboelectricity and resistivity. Pressure sensors are one of the promising sensing devices in sensing technology and are part of a broad field of mechanical sensors. Pressure sensors convert the force exerted on the object of interest into a measurable electrical signal that can be interpreted. Most of them are produced based on inductive, capacitive and piezoresistive phenomena which can be used to control and monitor pressure changes in many applications. Inductive pressure sensors require complex manufacturing techniques because it is difficult to form the materials into a coil shape. A capacitive pressure sensor uses a thin diaphragm as the capacitor plate and the changes experienced by the diaphragm due to pressure are converted into a signal by the transducer. Potential applications of capacitive sensors are in touchscreen panels. Another type of pressure sensor is the piezoelectric in which the pressure applied to the piezoelectric element is considered as a bidirectional transducer capable of converting stress into voltage and vice versa. Piezoresistive pressure sensor, on the other hand, pressure causes resistance changes across the piezoresistive element. The operation of these pressure sensors based on nanomaterials has the advantage of ease of manufacturing the devices with relatively low energy consumption in operation. AmongOther nanomaterials, carbon nanotubes (CNTs), graphene and its composites with piezoresistive elements have been studied by many researchers with different synthesis approaches. They stand out for their interesting thermal, electrical and mechanical properties, as well as their low density and high specific surface area at the nanoscale. Additionally, the advantage of using CNT-based piezoresistive pressure sensors instead of polysilicon-based pressure sensors is that the response of the CNT sensor is independent of temperature and they do not need to be products at high temperatures.The performance of these sensing materials depends critically on their microstructures, which in turn are affected by the processing techniques that prepare them for the desired products. Whether chemical or physical preparation has been followed, understanding how materials work at the nanoscale is of great importance for future technological applications. Since there are many nanomaterial-based pressure sensors available in this study, the main focus will be on the synthesis, characterization, and potential application of CNT-graphene-based pressure sensors. Synthesis techniques Nanomaterials can be synthesized using two approaches, the bottom-up method (CVD, electrochemical, sol-gel, solvothermal, etc.) where the material is synthesized atom by atom from the bottom, unlike the top-down method (milling, ablation laser, lithography, etc.) in which the material is synthesized from the mass. Generally, the most commonly used techniques to produce carbon nanotubes are (i) carbon arc discharge technique, (ii) laser ablation technique and (iii) chemical vapor deposition (CVD) technique ). These techniques have been successful in manufacturing large quantities of CNTs. Carbon arc discharge In carbon arc discharge technique, two carbon electrodes are used to generate an arc by direct current. The electrodes are placed in a vacuum chamber supplied with inert gas and the aim of which is to increase the rate of carbon deposition. Initially, the electrodes are separated until the pressure is stabilized in the chamber. Once the pressure has stabilized, the power supply is turned on (approximately 20 V), the positive electrode is brought closer to the negative to initiate an arc. During the arc, a high temperature plasma is formed and once the arc is stabilized, the electrodes are held approximately one millimeter apart while the CNTs are deposited on the negative electrode. The power supply is then cut off and the instrument is allowed to cool once a specific length is reached. . The important parameters to note in this technique are (i) the arc current and (ii) the optimum pressure of the inert gas in the chamber. This technique can produce high quality CNTs and some studies by Ebbesen and Ajayan have shown high quality MWNTs with diameters between 2 and 20 nm and lengths of several microns. They reported helium pressures of 500 Torr with a current set at 18 V and TEM analysis revealed that the MWNTs produced by the arc discharge technique were linked together by strong Van der Waals forces and that nanotubes were made of two or more carbon shells. uses the same principle as arc discharge, but intense laser pulses are used to abrade a carbon target. CNTs are formed in the presence of an inert gas and a catalyst with ablation of a carbon source. This technique makes high quality CNTs with pronounced chirality [15] but it and arc discharge have disadvantages compared to CVD, suchas uncontrollable process parameters, high byproduct yields as well as desired CNTs that become difficult to separate. Another disadvantage is that both techniques use harsh conditions to produce these CNTs and scaling is also a factor, so they become expensive as more energy is required to synthesize them in large quantities. Important parameters that determine the amount of CNTs produced and should be noted are the amount and type of catalyst, temperature, pressure, type of inert gas, and cooling systems near the carbon target. Chemical Vapor Deposition (CVD) This is the most preferred technique. due to its simplicity in producing CNTs, it is economically viable as growth occurs at low temperatures and at room temperature to enable scaling of CNTs. Tubes are synthesized by giving energy to hydrocarbons. The energy splits the molecule into reactive radical species with a temperature range of 550-750℃ and the reactive radicals diffuse to and bind to the substrate. This results in the formation of CNTs. The substrate is usually coated with transition metals such as Ni.or Fe which acts as a catalyst and ethylene, acetylene and methane are generally used as hydrocarbon sources. The metal catalyst reduces the hydrocarbons into simple compounds, then the metal nanoparticles dissolve the carbon until its solubility limit is reached. The dissolved carbonaceous material precipitates and progresses outward to produce a network of crystallized cylindrical structures. Characterization of carbon nanotube-based pressure sensors Scanning electron microscopy The surface morphology of pure CNTs can be analyzed using a scanning electron microscope. The SEM image of pure CNT is shown in Figure 1 below. The scale bar is 5 µm, as shown in Figure 1, the surface morphology of the pure CNT-based sample is not uniform. The CNTs are randomly aligned on the sample surface. Some CNTs appear to have a straight (red arrow) and curved (white arrow) shape, but most of them even have a circular shape (blue arrow), which shows that carbon nanotubes are flexible in nature. The flexibility of CNTs makes them suitable materials for sensing technology, particularly in pressure sensors. Resistance-pressure relationships The resistance-pressure relationships for pure CNTs are shown in Figure 3. It can be seen from Figure 3 that as the external uniaxial pressure increases from 0 kNm−2 to 0.183 kNm−2, the DC resistances of the pure CNT pressure sensor decrease from 1.5 kΩ to 0.3 kΩ respectively. This shows an 80% decrease in DC resistance for CNTs. The thickness of the fabricated sample is an important factor that affects the overall performance of the sample and impacts the resistivity and conductivity of composite materials. Therefore, it is important to emphasize that the thickness of the sample depends on the applied external pressure. Lower pressure is required to compress and deform the thinner sample and vice versa. Even under lower applied external pressure, a large increase in charge carrier concentration can completely fill the localized energy states present between HOMO-LUMO levels, which can lead to higher electrical conductivity and thus greater lower resistance of the samples. Moreover, the applied uniaxial external pressure can be transferred equally to any location of the thinnest CNT samples. Therefore, under the same applied external pressure,.